The present invention relates to an adjustable headbox for a paper machine. More particularly, the invention relates to an adjustable headbox for a paper machine having a distribution header part, a distribution pipe system part connected to the distribution header part in the flow path of the pulp stock, an equalizing part communicating with an air tank, a turbulence part following the equalizing part, and a lip cone part, or the equivalent, after the turbulence part.
Finnish Pat. No. 50260, which is the equivalent of U.S. Pat. No. 3,791,918, of the present inventor, discloses a headbox having a distribution pipe part after the distribution header. An intermediate chamber part follows the distribution pipe part and is followed by a lamellar part. A lip cone part is provided after the lamellar part. The lamellar part consists of a plurality of lamellae inclined relative to the vertical plane and located side by side, defining between each other turbulence passages having a trapezoidal cross-section.
The operation of the headbox disclosed in the aforedescribed Finnish patent has proven favorable in certain respects, but one of its drawbacks is its fixed construction. It is therefore impossible to change substantially the brand or quality of paper produced, or to achieve a fine adjustment of the headbox properties to conform exactly to the paper brand being produced, to the pulp stock quality, or to the machine speed, in paper machines having this headbox.
Earlier Finnish patent application Nos. 800018 and 801167, of the present inventor, disclose certain headbox designs with a cassette structure. These headbox designs represent a specific endeavor to use exchangeable cassette-like components for the pulp stock flow passage-confining components of the headbox, so that the headbox may be assembled of exchangeable components. It is thereby comparatively easy to alter the structure of the headbox when the product quality is changed. A construction of this type also renders the maintenance operations for the headbox and its cleaning easier than ever before.
The operation of the headbox equalizing chamber at the extremes of the optimum range presents problems regarding the maintaining of cleanliness and paper formation, since the flow region, having constant dimensions, cannot be adjusted in accordance with speed, pulp stock qualities, or use of fillers and chemical additions. The adjustable headbox of the present invention eliminates, or reduces to a satisfactory level, the drawbacks of the known headboxes.
The adjustable headbox of the present invention is also applicable to multi-ply headboxes. Thus, Finnish patent application No. 801587 of the present inventor discloses a multi-ply headbox for a paper machine, having two or more pulp suspension flow passages on top of each other. These pulp suspension flow passages come together in the region of the lip cone and comprise a distribution header part, a distribution pipe system part or the equivalent, and flow equalizing and turbulence parts. The novel aspect of this Finnish patent application is that a sturdy plate component provided with sets of flow apertures is provided between the flow equalizing part and the turbulence part. The turbulence part consists of a plurality of parallel plate lamellae or the equivalent, fixed to be stationary primarily by their front ends in connection with the plate component only. One or a plurality of intermediate plates, extending into the region of the lip part of the headbox, are provided between the sets of plate lamellae.